Ask anti-tax activist Grover Norquist about Sen. Tom Coburn’s willingness to consider tax increases as a part of a grand bargain with Democrats to rein in the deficit, and you’ll get an earful.&nbsp;

But the conservative Oklahoma Republican just shrugged Wednesday when asked to comment on attacks from Norquist, who is president of Americans for Tax Reform, an advocacy group that, at least until recently, had long enjoyed a powerful grip on GOP politicians. Even Coburn is a signatory to ATR’s “No Tax Pledge,” viewed as a must for any Republican running for office.&nbsp;

In an interview with Roll Call on Wednesday, Norquist unloaded on Coburn’s participation in the Senate’s bipartisan “gang of six” budget negotiations as well as his stance on the president’s deficit commission. He referred to the efforts of the gang of six as a sham, said the Senator was being used by Democrats to promote tax increases and accused the Oklahoman of being duplicitous in his previously stated opposition to tax increases.&nbsp;

Coburn, who cruised to a second Senate term in 2010 and has long been viewed as among the most conservative and inflexible lawmakers on Capitol Hill, said the scale and urgency of the federal budget crisis has made it necessary to consider compromises that he might not have earlier in his career. Fixing the problem now means accepting the fact that Republicans can’t have everything their own way, he said.

“Any American who truly understands this problem knows that we’re going to have to come together and solve it, and we can’t have it all our own way. That lack of insight hurts their position,” Coburn said.&nbsp;

Norquist disagrees.&nbsp;

“That’s a fiction he makes up to cover up the fact that he wants to break his word to the people of Oklahoma,” he said. “He doesn’t understand. That’s why he’s not a Reagan Republican.”

Norquist’s latest eruption at Coburn reveals a long-simmering tension between the Senator and some in Washington’s conservative activist and think-tank communities.&nbsp;

ATR has not been the only group to target the Oklahoman for his willingness to consider breaking with GOP orthodoxy on taxes. Heritage Action Network, an advocacy organization connected to the influential think tank Heritage Foundation, recently sent an email blast to conservatives nationwide, including in Oklahoma, urging them to “stop” the gang of six.

One political operative associated with a D.C.-based activist group said the perception of Coburn as an unwavering conservative stalwart has never been universally shared by the activist communities. Coburn is viewed by some as an insider and deal-maker as intent on getting votes as he is on holding the line on philosophical principles.&nbsp;

“I don’t know how large the gap is. But there’s definitely a gap in how he’s perceived on the inside versus the outside,” the political operative said. “He’s always been one to play ball, but in a hard line way.”

Coburn’s quiet falling out with the activist group began when he supported a health care reform plan that proposed changes in tax law that some conservatives, including Norquist, argued was a tax increase. The Coburn camp disagreed.

Meanwhile, Senate Minority Leader Mitch McConnell (R-Ky.) and Speaker John Boehner (R-Ohio) appear to be in line with Norquist’s position — indicating that tax increases of any kind are off the table — in their rhetorical gamesmanship over increasing the debt limit and coming to a budget agreement with the White House. And McConnell this week downplayed the gang of six talks, saying the real negotiations would be conducted by a bipartisan group that has been meeting with Vice President Joseph Biden.

Though Coburn has personally attempted to avoid battling his critics, his office has been quick to defend the Senator’s participation in the gang of six and his flexibility on tax increases if they are coupled with structural fiscal reforms and massive spending cuts.

Last week, Coburn spokesman John Hart emailed his press list a release titled, “Chuck Colson calls out Norquist for defending corporate welfare.” (Colson is a well-known conservative and religious commentator who was ensnared in President Richard Nixon’s Watergate scandal.)

Pressed to react to his spat with Norquist, Coburn said there has been much speculation about his budget negotiations, but that his critics know very little about them. In fact, the gang of six talks — based on the results of the deficit reduction commission that Coburn sat on — have yet to yield a document or deal of any kind.&nbsp;

Coburn said those opposed to the gang of six, and the possibility that it might reach a compromise on taxes and spending, do not understand the magnitude of the nation’s fiscal crisis.&nbsp;

“The real risk is, at what time are the decisions taken out of our hands and put in the hands of the international financial community,” Coburn said. “ATR may think that isn’t going to happen. But I can tell you, if we don’t fix our problems, 90 percent of the world’s economists say it is.”

The Senator’s supporters note that for years Coburn was virtually a lone voice in the Congress in opposition to earmarks and subsidies to favored industries — particularly the ethanol subsidies promoted by the agriculture lobby. Norquist, these Republicans say, has supported ethanol subsidies and — through his promotion of the K Street Project for GOP lobbyists in the 1990s — earmarks. Hart’s Colson email addressed the ethanol issue. Additionally, Coburn supporters like to point out Norquist’s past connections to convicted GOP lobbyist Jack Abramoff.

Norquist said he credits Coburn for his years-long opposition to earmarks but charged the Oklahoman’s supporters with mischaracterizing his stance on ethanol subsidies. Norquist said he favors ending the subsidy, but only if coupled with a tax cut to offset the revenue increase.&nbsp;

Though they are arguing over arcane tax and budget matters, the spat appears personal, too. One Republican operative sympathetic to Coburn essentially referred to a Norquist as a fraud whose sole priority is personal financial gain.

“A lot of the Republican revolution of 1994 going off track was Grover and the K Street Project. He represents the careerist Republican more interested in power,” this Republican said, adding that Norquist “is not a limited-government guy, he’s a Republican hack.”